What was the Drover's purpose before the Goo became a killing machine?

The original purpose of the Drover was blanket exploration of entire landmasses. Their rapid production and fast movement allowed groups of them to cover vast distances in a short time. Surprisingly, the Drover legs used to function rather well in the water, rotating to provide a propeller-like motion. This meant the Goo could chart both the land and the sea with relatively little investment. Though small, in large groups Drovers can shred an enemy in seconds.

Striders once had a noble purpose.

The first Striders accompanied groups of Drover as they spread across the land. While the Drover surveyed, the Strider collected DNA samples and recorded details of both flora and fauna for transportation back to the hive mind. Now, the Strider has abandoned its collection duties in favor of firing razor-sharp shards. These shards are capable of piercing deep into enemy flesh and armor. Once embedded, the nanites that make up the shard detonate themselves, causing internal damage.

Those aren't eyes on top of its head!

Originally, the Radiant recorded data on geological patterns, studying plate tectonics and minerals within the ground. While the large orbs on the top of the Radiant's stalks are called eyes, they actually don't see like a Human eye does. Instead, the Radiant "sees" variances in earth vibrations, as well as changes to mineral consistency and density. Today, the Radiant uses its unique vision to detect enemy movements in a large area around itself, even on high terrain.

The Destructor used to eat rocks. Well, sort of.

The Destructor's original purpose was one of demolition. Whenever a group of Drovers would be unable to progress to a certain section of a planet due to terrain. Destructors could easily bore holes into hardened rock or flatten entire plateaus, given enough time. This allowed Drovers to easily reach any point on the planet. The Destructors volatile weapon can easily melt through a structure's outer layer or a vehicle's armor, though it is relatively vulnerable itself to being destroyed.